There is disclosed herein an imaging member used in electrophotography having a charge transport layer with multiple concentrations of charge transport compounds. More particularly disclosed herein is an imaging member that has a photogenerating layer and a charge transport layer with one or more regions or layers. In each region or layer, the charge transport compounds are molecularly dispersed or dissolved in a polymer binder to form a solid solution. In the resulting charge transport layer, the region or layer closest in proximity to the photogenerating layer is in contiguous contact therewith and comprises the highest concentration of charge transport compounds in a solid solution. The concentration of the charge transport compounds decreases from the region or layer in closest proximity to the photogenerating layer to the upper regions or layers of the charge transport layer.
A typical electrophotographic imaging member device comprises at least one photoconductive insulating layer. It is imaged by uniformly depositing an electrostatic charge on the imaging surface of the electrophotographic imaging member and then exposing the imaging member to a pattern of activating electromagnetic radiation, such as, light which selectively dissipates the charge in the illuminated areas of the imaging member while leaving behind an electrostatic latent image in the non-illuminated areas. This electrostatic latent image may then be developed to form a visible image by depositing finely divided electroscopic marking toner particles on the imaging member surface. The resulting visible toner image can then be transferred to a suitable receiving member such as paper.
A number of current electrophotographic imaging members are, for example, the multilayered photoreceptors that, in a negative charging system, comprise a substrate support, an electrically conductive layer, an optional charge blocking layer, an optional adhesive layer, a charge generating layer, a charge transport layer, and optional protective or overcoating layer(s). The imaging members of multilayered photoreceptors can take several forms, for example, flexible belts, rigid drums, flexible scrolls, and etc. Flexible photoreceptor belts may either be seamed or seamless belts. An anti-curl layer may, for example, also be employed on the back side of the flexible substrate support, the side opposite to the electrically active layers, to achieve the desired photoreceptor belt flatness.
Multilayered photoreceptors, when functioning under electrophotographic imaging machine service conditions, do typically exhibit mechanical failures such as frictional abrasion, wear, and surface cracking. Surface cracking is unique only in belt photoreceptors and is induced either due to dynamic fatigue of the belt flexing over the supporting rollers of a machine belt support module or caused by exposure to airborne chemical contaminants as those photoreceptor segments directly bend over the rollers after periods of photoreceptor belt non-use during machine idling. These chemical contaminants include solvent vapors and corona species emitted by machine charging subsystems. Surface cracking can also be exacerbated by the combination of the effects provided by fatigue belt flexing and airborne chemical exposure. In fact, the problem of photoreceptor surface cracking is a critical mechanical issue seen in imaging members, particularly, in flexible belts, because the cracks manifest themselves into printout defects that seriously impact copy quality.